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Epidemiology of Infectious Diseases: Plague

Causal agent
An acute bacterial infection caused by Yersinia pestis.

Common clinical features
Bubonic plague (most common): enlarged, tender lymph nodes, fever, chills and prostration1.

Septicaemic plague: fever, chills, prostration, abdominal pain, shock and bleeding into skin and other organs1.

Pneumonic plague: fever, chills, cough, difficulty breathing and rapid shock and death if not treated early1.

Untreated bubonic plague has a case fatality rate of 50-90%.


  • Endemic in countries of Africa, Asia, the Americas and the former Soviet Union.
  • There have been 3 recorded pandemics throughout history. Most notably the 'Black Death' which originated in Central Asia in 1346 which is estimated to have caused 25 million deaths worldwide.
  • In 2003 2,118 cases and 182 deaths were reported worldwide, over 98% of which were reported in Africa.
  • The last reported outbreak of plague in the UK was in 1918.

Wild rodents (especially ground squirrels). Domestic pets may carry infected fleas.

Mode of transmission
Commonly through the bite of an infective flea. Other important modes of transmission include direct contact with infectious body fluids, handling of tissues of infected animals and inhalation of infectious respiratory droplets.  

Primary pneumonic plague is transmitted thorough inhalation of aerosolized infective droplets and can be spread from person to person.

Incubation period
Bubonic plague - 1- 6 days.
Pneumonic plague - 10-15 hours.

Period of Communicability
Fleas may remain infective for months.


  • Rapid diagnosis and treatment is indicated.
  • Streptomycin and tetracyclines or chloramphenicol are the drugs of choice. Treatment after 15 hours probably does not influence the course of pneumonic plague3.

Prevention and control

  • Plague vaccine is no longer available in the UK and is rarely indicated.
  •  Suspected cases should be considered highly infectious and should be strictly isolated3.
  • Contacts should be offered prophylaxis.


  1. Centers for Disease Control and Prevention. Plague Fact Sheet, 2005.
  2. Heymann D L, editor, Control of Communicable Disease Manual. 18th ed. American Public Health Association; 2004.
  3. Hawker J, Begg N, Blair I, Reintjes R, Weinberg J. Communicable Disease Control Handbook, Blackwell, 2005.

© CM Kirwan 2006